Trigger action on link state change

[Michael Ross]

Hi all,

i was wondering if there is any ready-made method to trigger an action as  
soon as a link changes state.
Along the lines of
	onifdown_em0="/run/this/script"
in rc.conf

Background:
Discussing physical data security with a client yesterday: The machine has  
to run 24/7. The filesystem is encrypted on boot, but this doesn't help a  
lot if anybody brings an AC generator to steal the machine *AND* the UPS.  
Best point in time to lock the machine I could think of was when somebody  
pulls the NIC cable.

Regards,

Michael